The SRT 6.1-liter HEMI engine is rated at 425 horsepower and 420 lb.-ft. of torque. These improvements were achieved using time-honored methods: add more cubic inches, increase compression ratio, redesign the cylinder heads, intake and exhaust systems for better flow, and increase engine speed. To employ these methods, SRT engineers modified or upgraded many components of the 5.7-liter HEMI engine to create the new 425-horsepower 6.1-liter HEMI.

SRT 6.1-liter HEMI engine block and lubrication system:

The basic, deep-skirted engine block structure is redesigned with reinforced bulkheads to handle higher loads. To get more air in and out of the cylinders, SRT engineers bored out the diameter of each cylinder by approximately 3.5 millimeters in order to increase the total displacement from 5.7 liters to 6.1 liters. Cylinders are honed with torque plates to ensure a truer bore, to reduce friction and increase power. Oil squirters, aimed at the underside of each piston, are added to aid piston cooling for engine durability. A special oil pump pressure relief valve is added to accommodate the squirter oil flow. The oil pan and windage tray are modified to manage oil return to the pan sump at high engine speeds and improve power.

SRT 6.1-liter HEMI piston assembly and crankshaft:

Larger-diameter, flat-top pistons with high-load capability are specified to handle the SRT 6.1-liter HEMI's compression ratio, which was increased to 10.3:1 from 9.6:1. Connecting rods are redesigned and make use of higher- strength powder metal material. New floating piston pins are introduced to handle higher loads. The SRT 6.1-liter HEMI's crankshaft is forged from micro alloy steel and rotates in tri-metal main bearings for high-load capability. The crankshaft damper is re-tuned for higher engine speeds.

Continuing its air-pumping efficiency, engine breathing in the SRT 6.1-liter HEMI is improved with specially designed intake and exhaust manifolds. The cast aluminum intake manifold is designed with shorter, larger- diameter and tapered runners for high-speed tuning. Internal runners are core-dipped to smooth the runner finish and improve air flow. Fuel injector flow capacity is also increased by 14 percent over the 5.7-liter engine. Electronic throttle control is shared with the 5.7-liter HEMI, but breathes through a revised high-flow air cleaner box outfitted with a tuned resonator delivering a deep performance sound character (and good for an extra eight horsepower). Exhaust headers on the SRT 6.1-liter HEMI are individual tubes encased in a stainless steel shell. Exhaust runners allow increased gas flow while maintaining fast catalyst light-off, while adding 12 horsepower over the 5.7- liter engine's cast manifolds. The net effect of the race-proven performance recipe of enhancements is to unleash more energy in the combustion process.

SRT 6.1-liter HEMI engine management system:

To control the combustion process, SRT engineers fine-tuned the engine management system using dual knock sensors with premium fuel. Air-fuel mixtures are ignited by two spark plugs, with platinum tips, in each cylinder. Spark plugs are fired by individual coils for each cylinder, sitting on isolated cylinder head covers, which are adorned with a traditional HEMI black wrinkle finish.

The bottom line:

The end result is an SRT 6.1-liter HEMI that makes 25 percent more horsepower than the 5.7-liter version in the Chrysler 300C, Dodge Magnum, and Ram Trucks, yet maintains the HEMI's reliability and durability, smooth idle quality, reasonable fuel economy, and meets EPA emissions standards.

I can tell you this, I installed several 5.7's into street rods including the red 70 Challenger convertable on the cver of Mopar Action (03) and at SEMA in (03) I also installed the 6.1/ 5 spd. in the 68 GTX ( actually a satalite) that went to SEMA in 05 also in Mopar action and Mopar muscle, and to answer your question the actual diff, is quite substantial!

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